UnixQT5.6 QSettings找不到QSettings::SystemScope配置文件

Question

链接到Qt报告：QTBUG-53313

从QT5.5转到Qt5.6是QSettings的一个问题，它在系统范围内找不到QSettings配置文件。在下面的main.cpp中，以各种方式初始化QSettings，然后查询其属性：

// File: main.cpp

#include <QApplication>
#include <QDebug>
#include <QSettings>
#include <QCoreApplication>

#define ASSUMED_SYSTEM_CONFIG "/etc/xdg/TheOrg/TheApp.conf"
#define ASSUMED_USER_CONFIG "/home/user/.config/TheOrg/TheApp.conf"

void print_info(const QSettings& settings, const char& use_case);

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QCoreApplication::setOrganizationName("TheOrg");
    QCoreApplication::setApplicationName("TheApp");

    QSettings settings_a;
    QSettings settings_b("TheOrg", "TheApp");
    QSettings settings_c(QSettings::SystemScope, "TheOrg", "TheApp");
    QSettings settings_d(QSettings::NativeFormat, QSettings::SystemScope, "TheOrg", "TheApp");

    print_info(settings_a, 'a');    
    print_info(settings_b, 'b');    
    print_info(settings_c, 'c');    
    print_info(settings_d, 'd');

    return a.exec();
}

void print_info(const QSettings& settings, const char& use_case)
{
    int value = settings.value("the_value").toInt();

    qDebug() << "Using case (" << use_case << ")";

    qDebug() << "The value is " << value;

    qDebug() << "Settings scope is: " << ((settings.scope() == QSettings::SystemScope) ? "System" : "User");
    qDebug() << "Settings organization is: " << settings.organizationName();
    qDebug() << "Settings application name is: " << settings.applicationName();
    qDebug() << "Settings fallbackEnabled is: " << settings.fallbacksEnabled();
    qDebug() << "Settings filename is: " << settings.fileName() << "\n";
}

ASSUMED_USER_CONFIG文件在系统中不存在。

ASSUMED_SYSTEM_CONFIG文件在系统中确实存在，并包含：

the_value = 42

使用QT5.5编译后，程序返回：

Using case ( a )
The value is  42
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( b )
The value is  42
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( c )
The value is  42
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/etc/xdg/TheOrg/TheApp.conf" 

Using case ( d )
The value is  42
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/etc/xdg/TheOrg/TheApp.conf" 

使用Qt5.6编译后，程序返回：

Using case ( a )
The value is  0
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( b )
The value is  0
Settings scope is:  User
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/.config/TheOrg/TheApp.conf" 

Using case ( c )
The value is  0
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/Qt5.6/5.6/gcc_64/etc/xdg/TheOrg/TheApp.conf" 

Using case ( d )
The value is  0
Settings scope is:  System
Settings organization is:  "TheOrg"
Settings application name is:  "TheApp"
Settings fallbackEnabled is:  true
Settings filename is:  "/home/user/Qt5.6/5.6/gcc_64/etc/xdg/TheOrg/TheApp.conf" 

这里有几个问题：

当使用QT5.5编译时，设置'filename‘将按照所有情况(a、b、c、d)的预期构造。大小写'a‘和'b’是ASSUMED_SYSTEM_CONFIG文件的ASSUMED_SYSTEM_CONFIG，因为ASSUMED_USER_CONFIG文件不存在。因此，“the_value”将正确地从设置文件中检索。

然而，当使用Qt5.6编译时，设置'filename‘似乎构造得不正确，例如'c’和'd‘(正确的路径被附加到"/home/user/Qt5.6/ 5.6 /gcc_64")。因此，不能从设置文件中检索“the_value”。

我没有覆盖Qt中的任何默认环境变量，Qt5.6是由Qt维护工具自动安装的。我知道我可以使用环境变量XDG_CONFIG_HOME来设置QSettings::SystemScope文件的绝对路径，但我认为我不应该这样做。

要重新声明主要问题，如何使用ASSUMED_SYSTEM_CONFIG文件(即QSettings::SystemScope)和QSettings？

还有其他人遇到过这种情况吗？我在两台不同的机器上测试过这个。

Answer 1

这是预编译linux二进制文件的一个问题。如果从源代码编译Qt5.6，则可以通过编译带有标志'-sysconfdir=/etc‘的Qt来避免此问题。

如果这不是一个选项，则可以设置环境变量XDG_CONFIG_HOME。

这个错误现在应该在QT5.6.1快照中修复。。